What is the wavelength of the sound waves?

[look416]

Homework Statement

a stationary sound wave has a series of nodes. The distance between the first and the sixth node is 30.0 cm. What is the wavelength of the sound waves?

Homework Equations

The Attempt at a Solution

well no idea about it
but in my attempt to solve it, i tried assuming 2L = $$\lambda$$
but there are 6 nodes so $$\lambda$$ = $$\frac{1}{3}$$L
by substituting the value of dist, i get $$\lambda$$ = 10cm
which is wrong. the ans is 12.0 cm
i wonder how to solve it

 

[joriarty]

Try drawing yourself a diagram of the problem (ie just draw a wave going through six nodes), you should be able to solve it a bit more easily once you can visualise it.

 

[joriarty]

Your current working is neglecting the fact that there are two nodes at either end of this hypothetical wave. (kind of analogous to a similar problem you are probably familiar with - ie if a farmer had 100m of wire to build a fence and he could place the posts 2m apart, how many posts would he need?)

 

[look416]

i think i know it
probably i should count the between one
so it should be $$\frac{2}{5}$$ L = $$\lambda$$
by computing it
i get 12.0 cm
yeah
thx all of you